Whether we think about problems or exercise, every moment consumes energy. Where does this energy come from? It comes from the oxidative combustion of the three major thermogenic nutrients in the human body. Food chemical energy is released through oxidative decomposition and stored in the high-energy compound adenosine triphosphate, which is used for various functional activities and body temperature maintenance in the human body, and most of the energy is eventually dissipated outside the body in the form of heat energy.
Sugar, protein and fat in food are the three major thermogenic nutrients, which oxidize and release energy in our body. Each gram of sugar is completely oxidized in the body to release 4 kcal of energy; Each gram of protein completely oxidized in the body also releases 4 kcal of energy; Lipids are high-calorie substances, and 9 kcal of energy are released by complete oxidation in the body per gram. 1 calorie is the heat absorbed by 1 gram of water from 15 ° C to 16 ° C, which is too small for the energy of the human body, so the commonly used unit is kcal. An apple weighing about 200 grams contains about 100 kcal.
The body's main source of energy is sugar, also known as carbohydrates. Sugar is a combination of sunlight, air and water converted by plants through photosynthesis. Commonly eaten sugars include starch in staple foods, glucose, sucrose and fructose in fruits and vegetables, and lactose in dairy products. These sugars are digested and absorbed and metabolized by the liver and finally present in the blood in the form of glucose, which is commonly known as "blood sugar". People usually think that sugar is sweet, but starch as a polysaccharide does not have sweetness, sweet is glucose, sucrose and fructose, these sugars are absorbed quickly, easy to raise blood sugar and cause blood sugar fluctuations, it is recommended to minimize intake. Natural sweet foods can be consumed in moderation, and the recommended amount of fruits is 200-400 grams per day.
Protein can also be used as a source of energy for the body, but it is relatively rare and precious, and is mainly used to synthesize human tissue.
Lipids are the most productive nutrients, converting into body fat to store energy. Usually, the human body rarely uses fat for energy, and uses fat when hungry or continuous exercise.
The three major thermogenic nutrients are the source of human energy, and what are the energy consumption of the human body? There are four main ways of energy expenditure: basal metabolism, physical activity, special motility of food, and growth and development.
Basal metabolic energy refers to the energy necessary for the body to maintain the most basic life activities and metabolism, that is, the energy metabolism of people under conditions such as awake, fasting, lying still, without tense mental activity and ambient temperature of about 25 °C. At this time, the human body still needs to maintain body temperature, the heart is still beating, breathing is still going on, and brain activity, nerve conduction, and muscle contraction are at the lowest level. The basal metabolic energy of the average person is about half of the energy consumption of the whole day, which means that if you do nothing for a day, the energy consumption is about half of the usual day.
Physical activity refers to the energy consumed by various types of labor and exercise. Muscle contraction is very energy-intensive, the greater the load on the muscles, the more energy is consumed, if the basic energy consumption is used when sitting, standing is 1.5 times, washing clothes is 3 times, running is 7 times, parallel bars are 24 times, pull-ups are 30 times; If you want to accurately calculate the amount of physical activity consumed in a day, you should monitor the various activities of the day, convert and add up the energy expended. Generally, the labor intensity is divided into 5 levels for estimation, office clerks are extremely light physical labor, steelmaking workers are heavy physical labor. Although mental work also consumes energy, there is not much difference between meditative thinking and casual thinking, so it is not regarded as one of the ways of energy consumption, but is classified as basic metabolic energy.
The special kinetic energy of food refers to the additional energy consumed due to food intake, including the energy consumption of food digestion, absorption and metabolism, which is equivalent to about 1/10 of the basal metabolic energy.
Growth and development energy is the energy consumed by children, adolescents, pregnant women, patients during the recovery period, etc., and each gram of new tissue synthesized consumes about 4.78 kcal of energy.
In summary, the daily energy consumption of adults with moderate labor intensity is about 2400-2700 kcal, and the specific energy consumption value should take into account factors such as age, gender, body size, genetics, etc., and cannot be generalized. If long-term energy intake is less than consumption, it will be emaciated or even malnourished; If long-term energy intake is greater than consumption, you will be overweight or even obese. Energy balance is a requirement for maintaining human health and survival, and it is usually necessary to ensure that the consumption and intake of energy within 5-7 days tend to be equal. If we have the right weight and a well-proportioned body, we should maintain energy balance, otherwise we should improve energy metabolism by adjusting diet and exercise to achieve the ideal weight.